Biology - How populations evolve

13.0 Biodiversity and Evolution

  • Biodiversity is the result of evolution.
  • The Sonoran Desert displays various species.
  • Over 1.8 million species have been identified, with more awaiting discovery.
  • Evolution explains life's diversity.
  • Evolution traces life's history back hundreds of millions of years.
  • Evolution is ongoing and influenced by the environment and human activities.
  • Understanding evolution is fundamental to biology.
  • The chapter will cover Charles Darwin's legacy and natural selection.

Darwin's Theory of Evolution

13.1 Darwin's Sea Voyage and Theory Formation

  • Charles Darwin's work significantly impacted biology.
  • His book, On the Origin of Species by Means of Natural Selection, marked the beginning of evolutionary biology.
  • Darwin was fascinated by nature, collecting insects, fishing, and hunting.
  • He initially studied medicine and then theology but returned to his interest in nature.
  • Prevailing views during Darwin's time included the belief that species are fixed and unchanging, influenced by Aristotle and Judeo-Christian culture.
  • Religious scholars estimated Earth to be 6,000 years old.
  • Darwin sailed on the HMS Beagle, which surveyed the South American coast.
  • He collected thousands of fossils and living specimens and kept detailed journals.
  • He observed the diversity of life and adaptations to different environments.
  • Geographic proximity was a better predictor of relationships than environmental similarity.
  • South American fossils resembled contemporary species of that continent.
  • Darwin proposed natural selection as the mechanism for evolution.
  • Natural Selection: Individuals with advantageous traits are more likely to survive and reproduce.
  • Adaptations: Accumulation of diverse modifications that fit organisms to specific ways of life.
  • Darwin was intrigued by the distribution of organisms on the Galapagos Islands.
  • The Galapagos Islands have unique species resembling South American species.
  • Examples: Galapagos marine iguanas and distinct varieties of giant tortoises.
  • Charles Lyell's Principles of Geology influenced Darwin.
  • Lyell's book proposed an ancient Earth shaped by gradual geological processes.
  • Darwin witnessed an earthquake in Chile, realizing Earth's surface changes gradually.
  • Fossils of marine snails in the Andes suggested uplift by mountain-building forces.
  • Descent with modification: Darwin's term for evolution where present-day species descend from ancient ancestors with accumulated differences.
  • Evolution: Accumulation of adaptation to various habits. Ancestral species diversify into descendant species.
  • Darwin's theory generated predictions tested and verified over 150 years.
  • Evolution by natural selection is a widely accepted scientific theory.
  • Evolution: Genetic changes in a population from generation to generation.

13.2 Fossil Evidence for Evolution

  • Fossils document differences between past and present organisms.
  • They show that many species have become extinct.
  • Hard parts of animals, rich in minerals, may remain as fossils (e.g., bones, teeth, shells).
  • Example: Fossilized skull of Homo erectus.
  • Some fossils are casts formed when organisms decompose in sediment, leaving a mold filled with minerals.
  • Fossils can also be imprints or footprints.
  • Entire organisms can be encased in amber or frozen in ice.
  • Fossils are often found in sedimentary rocks formed from layers of sediment called strata.
  • The relative ages of fossils are determined by the layer in which they are found.
  • Paleontologists study fossils and access old fossils through erosion.
  • Fossil record: Chronicle of evolution in rock strata.
  • The fossil record is incomplete but remarkably detailed.

13.3 Transitional Forms and Whale Evolution

  • Darwin predicted the existence of transitional forms linking different groups of organisms.
  • Example: Whale evolution from land-dwelling mammals.
  • Fossils show a series of changes in mammals adapted to aquatic habitats.
  • Whales (cetaceans) have forelimbs as flippers and lack hind limbs.
  • Transitional forms should have reduced hind limbs and pelvic bones.
  • Pakicetus: 50-million-year-old wolf-sized carnivore with cetacean middle ear structures.
  • Ambulocetus: 48-million-year-old intermediate with mobility on land and swimming adaptations.
  • Rodhocetus: 46-million-year-old with short limbs and webbed feet.
  • Dorudon: 40-35 million years ago, fully aquatic with paddle-like forelimbs and tiny hind limbs.
  • Molecular biologists found a close relationship between whales and hippopotamuses (cloven-hoofed mammals).
  • Pakicetus and Rodhocetus had ankle bones of cloven-hoofed mammals.
  • Evidence from different lines of inquiry converges to support the evolutionary origin of whales.

13.4 Homologies as Evidence for Evolution

  • Homology: Similarity resulting from common ancestry.
  • Evolution is descent with modification.
  • Related species have characteristics with underlying similarity but different functions.
  • Anatomical similarities among vertebrate forelimbs indicate common ancestry.
  • Homologous structures: Features with different functions but structural similarity due to common ancestry.
  • Advances in molecular biology provide deeper understanding of homologies.
  • Evolutionary history is documented in DNA.
  • Closely matching homologous genes indicate recent common ancestry.
  • Molecular comparisons help develop hypotheses about evolutionary divergence.
  • All life-forms share the same genetic language of DNA and RNA and a universal genetic code.
  • Molecular homologies extend beyond the shared genetic code.
  • Embryonic development reveals similarities not visible in adults (e.g., tails and pharyngeal pouches in vertebrate embryos).

13.5 Evolutionary Trees and Patterns of Descent

  • Darwin viewed life's history as a tree with branching from a common trunk.
  • Evolutionary tree: Diagram representing patterns of descent.
  • Homologous structures are used to determine branching sequence.
  • Recent characters are shared within smaller groups.
  • Tetrapods: Possess the same basic limb bone structure.
  • Branch points in evolutionary trees represent common ancestors.
  • Evolutionary trees are hypotheses supported by fossil, anatomical, and molecular data.

13.6 Natural Selection and Adaptation

  • Domesticated plants and animals are products of selective breeding from wild ancestors (artificial selection).
  • Artificial selection: Selective breeding to promote desirable traits.
  • Variation and heritability are essential components of artificial selection.
  • Variation: Differences among individuals.
  • Heritability: Transmission of traits from parent to offspring.
  • Darwin was a careful observer of variations.
  • Thomas Malthus's essay on human populations influenced Darwin.
  • Darwin deduced that limited resources lead to a struggle for existence.
  • Natural selection: Unequal reproduction where individuals with better traits survive and reproduce.
  • Over time, adaptations accumulate.
  • Natural selection can modify species over generations.
  • Three key points about evolution by natural selection:
    • Populations evolve, not individuals.
    • Natural selection amplifies or diminishes heritable traits only.
    • Evolution is not goal-directed and doesn't lead to perfectly adapted organisms.

13.7 Observing Natural Selection in Action

  • Adaptations suit organisms to their environment.
  • Evolutionary change can be observed in scientific studies.
  • Example: Peter and Rosemary Grant's study of finches on the Galapagos Islands.
  • Beak size changes depending on seed availability.
  • Evolution of pesticide resistance in insects is another example."